l Will this bill give the state new powers to spy on people's phone calls and emails?
No. The bill creates a legal basis for the continuation of existing police and security agency capabilities to access communications data and to intercept suspects' calls and emails. It will allow telecoms companies to retain data for 12 months, so that law enforcement agencies can use it while investigating serious crimes.
l What is the difference between communications data and intercepts?
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Communications data includes details of when, where and how individuals contacted one another electronically, but not the content of any calls or emails.
It has been used in 95 per cent of all serious organised crime cases handled by the Crown Prosecution Service and every major Security Service counter-terrorism investigation over the last decade.
Legal intercepts involve police or security agencies listening in to a specific suspect's calls or viewing the content of emails. Intercepts require a warrant signed by the Home Secretary in every case, and are subject to oversight by the Interception of Communications Commissioner.
l If there are no new powers, why do we need a bill at all?
A European Court of Justice ruling in April struck down an EU directive permitting the retention of data by telecomms companies, on privacy grounds.
Unlike other EU countries - such as Ireland and Denmark - Britain had implemented the directive through secondary legislation, rather than writing it into UK law with an Act of Parliament.
Without the directive, companies could start deleting data within weeks.
l Why is the bill being rushed through Parliament in three days?
The ECJ ruling comes into effect in the autumn, and the Prime Minister believes that the UK could face a "cliff edge" within weeks when data would start being deleted.
If the bill is not passed by the time Parliament goes into recess on July 22, it will be too late to act when MPs return from their long summer break in September.